A well known semiconductor memory component is a random access memory (RAM). RAM permits repeated read and write operations on memory elements. Typically, RAM devices are volatile, in that stored data is lost once the power source is disconnected or removed. Non-limiting examples of RAM devices include dynamic random access memory (DRAM), synchronized dynamic random access memory (SDRAM) and static random access memory (SRAM). In addition, DRAMS and SDRAMS also typically store data in capacitors which require periodic refreshing to maintain the stored data.
Recently resistance variable memory elements, which include programmable conductor memory elements, have been investigated for suitability as semi-volatile and non-volatile random access memory elements. Generally a programmable conductor memory element includes an insulating dielectric material formed of a chalcogenide glass disposed between two electrodes. A conductive material, such as silver, is incorporated into the dielectric material. The resistance of the dielectric material can be changed between high resistance and low resistance states. The programmable conductor memory is normally in a high resistance state when at rest. A write operation to a low resistance state is performed by applying a voltage potential across the two electrodes.
When set in a low resistance state, the state of the memory element will remain intact for minutes or longer after the voltage potentials are removed. Such material can be returned to its high resistance state by applying a reverse voltage potential between the electrodes as used to write the element to the low resistance state. Again, the highly resistive state is maintained once the voltage potential is removed. This way, such a device can function, for example, as a resistance variable memory element having two resistance states, which can define two logic states.
One preferred resistance variable material comprises a chalcogenide glass, for example, a GexSe100−x glass. One method of forming a resistance variable memory element based on chalcogenide glass includes forming a lower electrode over a substrate, forming an insulating layer over the lower electrode, forming an opening in the insulating layer to expose the lower electrode, forming a metal containing chalcogenide glass in the opening, recessing the metal containing chalcogenide glass, and forming an upper electrode overlying the insulating layer and the recessed metal containing chalcogenide glass. The resistance variable memory element can be recessed using a dry etch or plasma etch. The chemistries used in the dry etch or plasma etch produce inherent sidewalls of chemical compounds on the photo resist or structure used to define the etch which are very difficult to remove.
A specific example of a metal containing chalcogenide glass is germanium-selenide (GexSe100-x) containing silver (Ag). A method of providing silver to the germanium-selenide composition is to initially form a germanium-selenide glass and then deposit a thin layer of silver upon the glass, for example by sputtering, physical vapor deposition, or other known technique in the art. The layer of silver may be irradiated, preferably with electromagnetic energy at a wavelength less than 600 nanometers, so that the energy passes through the silver and to the silver/glass interface, to break a chalcogenide bond of the chalcogenide material such that the glass is doped with silver. Silver may also be provided to the glass by processing the glass with silver, as in the case of a silver-germanium-selenide glass. Another method for providing metal to the glass is to provide a layer of silver-selenide on a germanium-selenide glass.
It would be desirable to have an improved method of fabricating a resistance variable memory element, which does not produce undesirable etch chemistry sidewalls.